A mounting device for supporting a car engine in a chassis in such a way as to prevent vibration, comprising a piezoelectric element which deforms according to an applied voltage, has been disclosed in Tokkai Sho 59-23139, Tokkai Sho 59-23140 and Tokkai Hei 1-114522 published by the Japanese Patent Office.
In these mounting devices, piezoelectric elements and rubber vibration absorbers are arranged in series between flanges, and fixed between the engine and the chassis by means of bolts.
The piezoelectric element elongates in an axial direction when a voltage is applied to it. By causing the element to elongate and contract in synchronism with the frequency of a vibration so as to oppose the displacement of the engine which would be produced by the vibration, therefore, the vibration of the engine can be prevented.
However, these mounting devices consist of active damping means, i.e. the piezoelectric element, and passive damping means, i.e. the rubber vibration absorbers, arranged in series. Part of the damping effect of the active damping means is therefore absorbed by the rubber vibration absorbers, and the overall damping effect has consequently been impaired by a corresponding amount.
Displacements of the engine, which are the cause of engine noise or acceleration noise, are generally of the order of 100 .mu.m. If a piezoelectric element having a distortion of 0.1% or less is used to prevent this vibration, the length of the element should be at least 10 cm. The size of the device therefore reaches unsuitably large proportions for mounting in automobile engines.